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Prime Minister John Key will be in Greymouth next week to apologise personally to the Pike River Mine families.

A letter detailing the apology was delivered to the families of the 29 men yesterday, the same day Mr Key reacted angrily to questions in Parliament about his support for the families' mine re-entry proposal.

West Coast-Tasman MP Damien O'Connor said afterwards the Prime Minister had "overreacted" to a simple question.

"I asked John Key whether he would abide by his commitment that the recovery of the miners' bodies would remain an 'absolute priority' and that the money for recovery was 'no object'. He chose to respond very angrily," Mr O'Connor said.

However, Mr Key has written to the families, noting that the Royal Commission's report into the 2010 disaster had painted a disturbing picture of corporate and regulatory failure. He has also arranged to meet with them again, in Greymouth next Thursday.

"On behalf of the Government, I want to reiterate my apology to the families, friends and loved ones of the deceased men for the role this lack of regulatory effectiveness played in the tragedy," he wrote.

He said he "deeply regretted" the loss of life and the suffering caused.

Commenting on the body recovery operation, he said a focus on exploring the drift (main tunnel) appeared a potentially realistic goal.

"If a safe, technically feasibly and financially credible plan for exploration of the drift can be developed the Government would be willing to contribute funds, provided the plan has been prepared by, or has the support of Solid Energy, and provided it satisfies the requirements of the High Hazards Unit."

Mr Key told the families he hoped the Royal Commission had provided them with answers, "at least in some small way to achieve some closure".